scripts: codemap[d3].py: Added --tile-* for tiling by stack/ctx/etc

This replaces the previous fallback-to-what's-available behavior with
explicit flags:

- --tile-code - Tile based on code size (the default)
- --tile-stack - Tile based on stack limits
- --tile-frames - Tile based on stack frames
- --tile-ctx - Tile based on function context
- --tile-1 - Tile functions evenly

This has the benefit of 1. being easier to toggle, 2. being explicit,
and 3. allowing code/stack/ctx in punescapes (titles, labels, etc).

There is an interesting question if --no-stack should be implicit, since
showing two stack treemaps may be confusing, but I think that's trying
to be too clever. Instead I just added the -S/--no-stack shortform to
make it easier to toggle.

Also updated ctx.py's description string. Probably need to check what
else is out of date in other scripts as well.

scripts/ctx.py

@@ -1392,7 +1392,7 @@ if __name__ == "__main__":
     import argparse
     import sys
     parser = argparse.ArgumentParser(
-            description="Find struct sizes.",
+            description="Find the overhead of function contexts.",
             allow_abbrev=False)
     parser.add_argument(
             'obj_paths',